This invention relates to a lap edge sealant composition for sealing the lap joints of roofing materials, and more particularly, to a lap edge sealant having a high solids content and a low volatile organic compound (VOC) content.
In the field of single-ply commercial rubber roofing, sheets of roofing material are typically laid on a roof in an overlapping fashion and spliced together to form a continuous sheet which covers the roof Lap joints are typically used to splice adjacent sheets of roofing material together. The exposed seams of the lap joints are then sealed with an adhesive, typically, a caulking compound, to act as an additional seal to prevent penetration of moisture along the external seam. Currently, solvent-based adhesive sealants are used for sealing the lap joints of adjacent sheets of membrane roofing materials. Such sealants typically utilize aromatic solvents such as benzene, toluene, xylene, etc. However, such solvent-based sealants are environmentally undesirable as they typically contain over 350 grams per liter (3 pounds per gallon) of volatile organic compounds. Because of environmental concerns, many states are beginning to mandate products having no more than 250 grams per liter (2 pounds per gallon) of volatile organic compound (VOC) content.
Another disadvantage of solvent-based sealants currently in use is their low solids content, i.e., about 20 to 30%. As such sealants typically cure by solvent evaporation, high shrinkage (typically about 40-60%) can occur when using these sealants. As a consequence, the cured films may exhibit fissure-type cracking and degradation after long term outdoor exposure.
A number of adhesives have been developed which exhibit lower VOC levels. For example, Congelio et al., U.S. Pat. No. 5,817,708, teach a low VOC content (less than 250 g/l) solvent-based adhesive for use in joining thermoplastic materials. Patel et al., U.S. Pat. No. 5,495,040, also teaches a low VOC (less than 250 g/l) solvent-based adhesive for joining ABS molded articles. However, such adhesives are not specifically formulated for use as lap edge roofing sealants, nor do they have a high solids content.
Backenstow et al., U.S. Pat. No. 4,849,268 teach a 100% solids sealant for providing an internal seal to spliced roofing membranes which is formed from EPDM, butyl or silicone based caulking compositions. The sealant is applied in combination with a splicing cement to the internal portion of the splice. However, Backenstow et al. require that the sealant, splicing cement, and roofing membrane be compatible in order to avoid separation of the sealant from the cement. In addition, Backenstow et al. do not seal the exterior seam on the lap joint.
Accordingly, there is still a need in the art for a lap edge sealant which effectively seals the external lap joints of adjacent sheets of membrane roofing material, which has a high solids content, a low VOC content, and which exhibits low shrinkage upon curing.
The present invention meets those needs by providing a lap edge sealant composition having a high solids content, a low VOC content of less than 250 g/l, and which exhibits no more than about 35% shrinkage upon curing. By shrinkage, it is meant the decrease in volume of the sealant after curing. The sealant composition provides excellent adhesion to a variety of roofing materials such as EPDM.
In accordance with one aspect of the present invention, a lap edge sealant composition for sealing the lap joints of roofing materials is provided comprising a rubbery polymer, a thermoplastic rubber, a tackifier, and a solvent, where the composition has a solids content of from about 65 to 90% and a VOC content of less than about 250 g/l.
Preferably, the rubbery polymer comprises EPDM. The thermoplastic rubber preferably comprises a styrene-ethylene/propylene copolymer.
The tackifier is preferably selected from the group consisting of aliphatic hydrocarbon resins, polybutene, and combinations thereof.
The solvent is preferably selected from the group consisting of aliphatic hydrocarbons, para-chlorobenzotrifluoride, and blends thereof. The aliphatic hydrocarbons are preferably selected from the group consisting of n-pentane, n-hexane, n-heptane, n-octane, and naphtha. The naphtha may comprise high flash naphtha solvent or VMandP (Varnish Makers and Painters) naphtha. In one preferred embodiment of the invention, the solvent comprises from about 26% by weight para-chlorobenzotrifluoride and from about 74% by weight VMandP naphtha. In another preferred embodiment, the solvent comprises from about 33% high flash naphtha and 67% VMandP naphtha.
The sealant composition also preferably includes an accelerator/cure package, which preferably comprises a mixture of a sulfur-containing composition and zinc oxide.
In a preferred form, the sealant composition comprises: a) from about 3 to 6% by weight of a rubbery polymer; b) from about 1 to 5% by weight of a thermoplastic rubber; c) from about 1 to 10% by weight of a tackifier; d) from about 30 to 50% by weight of a filler; and e) and from about 5 to 35% by weight of a solvent.
The sealant composition of the present invention may be applied at a job site under a variety of weather conditions to the lap joints of overlapping sheets roofing materials such as EPDM. The sealant composition exhibits low shrinkage upon curing, i.e., less than about 35%.
Accordingly, it is a feature of the present invention to provide a lap edge sealant having a high solids content, a low VOC content, and which exhibits low shrinkage upon curing. Other features and advantages of the invention will be apparent from the following detailed description, the accompanying drawing, and the appended claims.